The largest chunk yet of a meteor that exploded over Wisconsin last month
has been found by intrepid space rock hunters. But the remnant, which broke
into three pieces after hitting the ground, is still small enough to fit in the
palm of your hand.

Marvin Killgore, the
curator of meteorites for the Lunar and Planetary Laboratory at the University
of Arizona, and his wife, Kitty, arrived in Mineral Point, Wisc., just days after the
April 14 fireball
sighting, and now have a 10.6-ounce (300-gram) chunk of space rock that may
be the largest piece of the meteor found so far.

On April 14, people in southwestern Wisconsin and northern Iowa bore witness
to a sonic boom and fireball that briefly lit up the late evening sky. The
object, an ancient rock from space, entered the Earth's atmosphere as a ball of
flames after a 4.5 billion year journey through the solar system.

NASA officials estimated that the meteorite, which measured about 3.3 feet
(1 meter) across, exploded with a force equivalent to 20 tons of TNT.

Meteorite hunters from around the world quickly flocked to the Wisconsin farm
community that has become ground zero for the meteor fall to try to get their
hands on a piece of the debris. A farmer discovered the first
fireball fragment the morning after it exploded.

The Killgores found
their fragment on a road near a local candle factory. The rock was split into
three pieces on impact, and was even marked by the gravel road where it landed.

The Killgores' space
rock is a breccia – a conglomeration of rock fragments cemented
together. It most likely originated in the asteroid
belt that orbits the sun between Mars and Jupiter.

"This
one is relatively pristine, handled by very few human hands," Killgore said. "And it
hasn't been on Earth all that long. It's exciting to be the first one to see
something like this, to pick it up and hold it in your hand, and to know that
it just came from somewhere away from here. It's
pretty awesome."

There are likely other larger fragments of the Wisconsin meteor still out
there that will be found in the coming years, Killgore said, but these pieces will also be more
weathered.

The Killgores work with
Marc Fries, a scientist at NASA's Jet Propulsion Laboratory in Pasadena,
Calif., to locate meteorite fragments. Using Doppler weather radar maps, they
can triangulate the trajectory of objects that make it through Earth's
atmosphere and reach the ground.

Since exploding
meteors create clouds of debris (similar to atmospheric clouds) that are
picked up by radar sensors, the area where pieces of the meteorite land can be
detected using these meteorological devices.

"The pieces can fall anywhere," Killgore said. "It's basically like tossing a
handful of gravel into the grass and then see
if you can find them."

The meteorite-hunting duo has already amassed one
of the largest collections of meteorites in the world, with their heftiest find
weighing a staggering 1,600 pounds (726 kg).

A different sample from the meteorite had been previously found by a local
farmer, who sent it to the University of Wisconsin for examination. It was
found to contain traces of magnesium, iron and silica compounds, in addition to
other common minerals such as iron-nickel metal and iron sulfide.